1. Field of the Invention
The invention relates in general to a video recording device and a video recording method, and more particularly to a video recording device and a video recording method of automatically adjusting a focus parameter.
2. Description of the Related Art
More and more electronic devices (hereinafter referred to as video recording devices), such as digital cameras or mobile phones, provide recording functions. When the user continuously uses the recording function, a relative distance between the to-be-captured target and the video recording device may change during recording.
FIG. 1 is a schematic view showing a relative distance change between a to-be-captured target and a video recording device. Referring to FIG. 1, assuming a position of a to-be-captured target 4 is on the top of FIG. 1 at a first time point t1, and then the to-be-captured target 4 moves to the left side of FIG. 1 at a second time point t2. The relative distance (d) between the to-be-captured target 4 and the video recording device 3 is also correspondingly changed from a first distance D1 to a second distance D2. With the change of the relative distance (d), the zoom lens inside the video recording device 3 also needs to adjust its focus parameter so as to record the clear capturing picture.
In addition to the condition of FIG. 1, the zoom lens may also be affected by position of the user, who holds the video recording device and moves to another position, and cannot record the clear capturing picture because the relative distance between the to-be-captured target 4 and the video recording device 3 is changed. Alternatively, when the user changes the to-be-captured target (e.g., from the first to-be-captured target to the second to-be-captured target) upon recording, the zoom lens also needs to perform the corresponding adjustment because the relative distance between the video recording device and the first to-be-captured target is different from the relative distance between the video recording device and the second to-be-captured target.
In order to make the recording effect become clearer, many video recording devices provide the continue autofocus (hereinafter referred to as CAF) functions. In short, in the video recording device with the continue autofocus function, the position of the zoom lens is continuously adjusted with the movement of the to-be-captured target 4. Incidentally, the focal length of the zoom lens will be adjusted to the settings such that the to-be-captured target is clearly displayed.
During recording, the video recording device with the continue autofocus function needs to dynamically adjust the position of the zoom lens in correspondence with the movement of the to-be-captured target, and thus to find the suitable focal length. The process of dynamically adjusting the zoom lens needs to continuously change the position of the zoom lens. When the position of the zoom lens is adjusted, the video recording device 3 still needs to perform the recording through the zoom lens. Consequently, in the process of continuously recording, the method of dynamically adjusting the position of the zoom lens will cause the jitter phenomenon in the recording content.